Ideas for "Extra" Room in Dream Rental?

Q: We recently found our dream rental: an updated and spacious brownstone on a gorgeous city block. The ONLY problem is, there is an extra upstairs living room/bedroom/whatever-you-can-think-of room that needs some lovin'. It's the only carpeted room in the house, and we're vaguely planning to make it an extra living room.

The cons: the green walls, the carpet, and the shape. We're planning to paint the walls to start, but since it's a rental we'll have to work with the carpeting. The pros: the exposed brick, the 3 huge windows, the chair railing, and the built-in bench below one of the windows. We are working on a budget, and for right now our only plan is to paint the room a lighter, less bold color and to remove the existing curtains to expose the beauty of the windows. Any ideas on how to get the most out of our space and make this a room we love?